Co-channel wireless communication methods and systems using nonsymmetrical alphabets

ABSTRACT

Wireless communications are transmitted from at least two radioterminals to a base station co-channel over a return link using a return link alphabet. Wireless communications are also transmitted from the base station to the at least two radioterminals over a forward link using a forward link alphabet that has more symbols than the return link alphabet. The co-channel signals are deciphered at the receiver, while the radioterminals can use a smaller return link alphabet, which can reduce the power dissipation at the radioterminals.

[0001] CROSS-REFERENCE TO PROVISIONAL APPLICATIONS

[0002] This application claims the benefit of Provisional ApplicationSerial No. 60/457,043, entitled Satellite Assisted Push-To-SendRadiotelephone Systems and Methods, filed Mar. 24, 2003; ProvisionalApplication Serial No. 60/457,118, entitled Radio FrequencyCommunication Systems and Methods That Use Polarization Orthogonality toDouble Channel Capacity, filed Mar. 24, 2003; Provisional ApplicationSerial No. 60/473,959, entitled Systems and Methods That EnableCo-Channel Communications With a Base Station of a Plurality ofRadioterminals, filed May 28, 2003; and Provisional Application SerialNo. 60/477,522, entitled Satellite Assisted Push-To-Send RadioterminalSystems, Methods and Protocols, filed Jun. 11, 2003, all of which areassigned to the assignee of the present invention, the disclosures ofall of which are hereby incorporated herein by reference in theirentirety as if set forth fully herein.

FIELD OF THE INVENTION

[0003] This invention relates to wireless communications methods andsystems, and more particularly to wireless communication systems andmethods that can communicate co-channel.

BACKGROUND OF THE INVENTION

[0004] Polarization diversity receiving systems and methods are wellknown in wireless communications. For example, a wireless terminal maytransmit a linearly-polarized signal that may be received byorthogonally polarized antennas (e.g., horizontal and verticalpolarization) at a base station (terrestrial or space-based) to therebyseparately receive orthogonally polarized portions of the transmittedsignal. The orthogonally polarized portions may be combined toeffectively increase link robustness, since many channel degradationssuch as fading, are largely uncorrelated when comparing antennas oforthogonal polarizations. See for example, U.S. Pat. No. 6,526,278 toHanson et al. entitled Mobile Satellite Communication System UtilizingPolarization Diversity Combining; U.S. Pat. No. 5,724,666 to Dententitled Polarization Diversity Phased Array Cellular Base Station andAssociated Methods; U.S. Pat. No. 6,418,316 to Hildebrand et al.entitled Increasing Channel Capacity of Wireless Local Loop viaPolarization Diversity Antenna Distribution Scheme; and U.S. Pat. No.6,445,926 to Boch et al. entitled Use of Sectorized PolarizationDiversity as a Means ofIncreasing Capacity in Cellular Wireless Systems.

[0005] Other systems and methods that use polarization effects inwireless communications are described in the following publications:Andrews et al., Tripling the Capacity of Wireless Communications UsingElectromagnetic Polarization, Nature, Vol. 409, Jan. 18, 2001, pp.316-318; Wolniansky et al., V-BLAST: An Architecture for Realizing VeryHigh Data Rates Over the Rich-Scattering Wireless Channel, Invitedpaper, Proc. ISSSE-98, Pisa, Italy, Sep. 29, 1998, pp. 295-300; andCusani et al., A Simple Polarization-Recovery Algorithm forDual-Polarized Cellular Mobile-Radio Systems in Time-Variant FadedEnvironments, IEEE Transactions in Vehicular Technology, Vol. 49, No. 1,Jan. 2000, pp. 220-228.

[0006] It is also known to use diversity concepts to increase thecapacity of wireless communications. See, for example, the followingpublications: Miller et al., Estimation of Co-Channel Signals WithLinear Complexity, IEEE Transactions on Communications, Vol. 49, No. 11,Nov. 2001, pp. 1997-2005; and Wong et al., Performance EnhancementofMultiuser MIMO Wireless Communications Systems, IEEE Transactions onCommunications, Vol. 50, No. 12, Dec. 2002, pp. 1960-1970.

SUMMARY OF THE INVENTION

[0007] Some embodiments of the present invention transmit wirelesscommunications from at least two radioterminals to a base stationco-channel over a return link using a return link alphabet, and transmitwireless communications from the base station to the at least tworadioterminals over a forward link using a forward link alphabet thathas more symbols than the return link alphabet. As used herein, the term“co-channel” indicates signals that overlap in time and space, and thatuse the same carrier frequency, the same time slot if the signals areTime Division Multiple Access (TDMA) signals, and the same spreadingcode if the signals are Code Division Multiple Access (CDMA) signals,such that the two signals collide at a receiver. Embodiments of thepresent invention can allow the co-channel signals to be decoded ordeciphered at the receiver, and can allow the radioterminals to use asmaller return link alphabet which can reduce the power dissipation atthe radioterminals.

[0008] In some embodiments of the present invention, the wirelesscommunications are transmitted from the base station to theradioterminals non-co-channel over the forward link using the forwardlink alphabet that has more symbols than the return link alphabet. Inyet other embodiments, co-channel transmissions may be used. In someembodiments, wireless communications are transmitted from the at leasttwo radioterminals to at least one antenna at the base stationco-channel over a return link using a return link alphabet. In otherembodiments, these transmissions are made to at least onemultiple-polarized antenna at the base station. In yet otherembodiments, these transmissions are made to a plurality ofmultiple-polarized antennas at the base station. In still otherembodiments, these transmissions are made to a plurality ofmultiple-polarized antennas in a single sector of the base station. Insome embodiments, the wireless communications are transmitted to theplurality of multiple-polarized antennas in a sector if the at least tworadioterminals are separated by more than a predetermined distance. Inother embodiments, these transmissions are made to at least onemultiple-polarized antenna in at least two sectors of the base station.In yet other embodiments, these transmissions are made to at least onemultiple-polarized antenna at a first base station and at least onemultiple-polarized antenna at a second base station. In still otherembodiments, these transmissions are made from a singlelinearly-polarized antenna at each of the at least two radioterminals.

[0009] Other embodiments of the present invention transmit wirelesscommunications from at least two radioterminals to a base station over areturn link using a return alphabet and transmit wireless communicationsfrom the base station to the at least two radioterrninals co-channelover a forward link using a forward link alphabet that has more symbolsthan the return link alphabet. In other embodiments, as was describedabove, the transmission from the radioterminals to the base station maybe non-co-channel or co-channel. Moreover, the wireless communicationsmay be transmitted from the base station to at least one antenna at eachof the at least two radioterminals, to at least one multiple-polarizedantenna at each of the at least two radioterminals and/or to a pluralityof multiple-polarized antennas at each of the at least tworadioterminals, co-channel over a forward link using a forward linkalphabet that has more symbols than the return link alphabet, as wasdescribed above. Transmission from the base station may use at least oneantenna, at least one linearly-polarized antenna, at least twolinearly-polarized antennas, at least two linearly-polarized antennas ina sector, at least one linearly-polarized antenna in at least twosectors and/or at least one linearly-polarized antenna at two or morebase stations, as was described above.

[0010] In other embodiments of the present invention, wirelesscommunications are received from a base station at a first radioterminaland at least one second radioterminal that is proximate the firstradioterminal over a forward link, co-channel. The wirelesscommunications are relayed from the at least one second radioterminal tothe first radioterminal over a short-range wireless link. The wirelesscommunications that are relayed to the first radioterminal from the atleast one second radioterminal over the short-range wireless link areused to process the wireless communications that are received from thebase station at the first radioterminal. Moreover, these embodiments maybe combined with any of the embodiments that were described above.

[0011] Still other embodiments of the present invention bidirectionallytransmit wireless communications co-channel in time division duplex fromat least two radioterminals to a base station over a return link using areturn link alphabet, and from the base station to the at least tworadioterminals over a forward link using a forward link alphabet thathas more symbols than the return link alphabet. These embodiments alsomay be combined with any of the embodiments that were described above.

[0012] It will be understood by those having skill in the art thatembodiments of the present invention were described above primarily withrespect to method aspects. However, other embodiments of the presentinvention provide systems, base stations and radioterminals according toany of the embodiments that were described above.

BRIEF DESCRIPTION OF THE DRAWINGS

[0013]FIGS. 1-3 and 4A-4B are diagrams of co-channel wirelesscommunications according to various embodiments of the presentinvention.

[0014]FIG. 5A is a diagram of radioterminal to base stationcommunications according to embodiments of the present invention.

[0015]FIG. 5B is a diagram of base station toradioterminal-communications according to embodiments of the presentinvention.

[0016]FIG. 5C is a diagram of base station to radioterminalcommunications according to other embodiments of the present invention.

[0017]FIGS. 6A-6B are block diagrams of receivers that may be used inFIGS. 5A-5C according to embodiments of the present invention.

[0018]FIG. 7 graphically illustrates simulated receiver performance forsignals in Rayleigh fading channels according to some embodiments of thepresent invention.

[0019]FIG. 8 is a diagram of base station to radioterminal bidirectionalcommunications according to embodiments of the present invention.

[0020]FIG. 9 is a block diagram of a receiver and transmitter that maybe used in embodiments of FIG. 8.

[0021]FIG. 10 is a block diagram of a receiver that may be used in FIG.9 according to embodiments of the present invention.

[0022]FIG. 11 is a block diagram of a transmitter that may be used inFIG. 9 according to embodiments of the present invention.

[0023]FIGS. 12 and 13 are diagrams of radioterminals and base stations,respectively, according to embodiments of the present invention.

DETAILED DESCRIPTION

[0024] The present invention now will be described more fullyhereinafter with reference to the accompanying drawings, in whichembodiments of the invention are shown. This invention may, however, beembodied in many different forms and should not be construed as limitedto the embodiments set forth herein. Rather, these embodiments areprovided so that this disclosure will be thorough and complete, and willfully convey the scope of the invention to those skilled in the art.Like numbers refer to like elements throughout.

[0025] Some embodiments of the present invention may arise from arecognition that it is possible to configure two physically distinctradioterminals to transmit to a base station, also referred to as a basetransceiver station (BTS), co-channel, using the same return-linkradio-channel resource(s) while still being able, at the BTS, toreliably demodulate and reconstruct (i.e., decode) the two data streamsof the two physically distinct radioterminals. It is also possible toconfigure a BTS to transmit to two physically distinct radioterminalsco-channel, over the same forward-link radio-channel resource(s), whileeach of the two distinct radioterminals is able to reliably demodulateand reconstruct the information intended for it. The two physicallydistinct radioterminals may thus communicate bi-directionally with aBTS, co-channel, in some embodiments, using no more channel resource(s)than a single radioterminal would use. The signal processing techniquesthat make this possible, according to some embodiments of the invention,can exploit the multipath scattering nature of the radiochannel and/orthe multi-dimensional nature of space and its relationship toelectromagnetic wave propagation. Moreover, embodiments of the inventioncan be extended to allow three or more physically distinctradioterminals to communicate co-channel with a BTS without using anymore radiochannel resource(s) than a single radioterminal would.

[0026] Some embodiments of the present invention may also arise from arecognition that co-channel communications may be more beneficial for aninfrastructure (base station) receiver than for a radioterminalreceiver, because an infrastructure transmitter may not be power limitedand may thus resort to a higher-alphabet modulation format (i.e. 8-PSK,16-QAM, 64-QAM, etc.) to increase channel capacity on a forward link. Incontrast, a radioterminal's transmitter may be power limited and maythus be constrained to lower-alphabet modulation formats (i.e. QPSK,GMSK, etc.). Thus, the ability of two or more radioterminals to sendinformation to an infrastructure element (base station) co-channel maybe used advantageously to increase channel capacity on the returnlink(s). According to some embodiments, therefore, base stations andradioterminals may be configured to utilize different modulationalphabets on forward and return links with a return link alphabet havinga smaller number of distinct states (symbols) than a forward linkalphabet, and with at least some infrastructure (base station) receiversof the system configured for co-channel communications, as will bedescribed in further detail below.

[0027]FIG. 1 is a diagram of co-channel wireless communications usingnonsymmetrical alphabets according to some embodiments of the presentinvention. As shown in FIG. 1, wireless communications are transmittedfrom at least two radioterminals 110 a and 110 b to a base station (BTS)120 co-channel over a return link 130 using a return link alphabethaving return link symbols S_(R). As also shown in FIG. 1, wirelesscommunications are transmitted from the base station 120 to the at leasttwo radioterminals 110 a and 110 b over a forward link 140 using aforward link alphabet having forward link symbols S_(F), wherein theforward link alphabet has more symbols than the return link alphabet. Inother words, S_(F)>S_(R). In some embodiments, the wirelesscommunications are transmitted from the base station 120 to the at leasttwo radioterminals 110 a and 110 b non-co-channel over the forward link140 using the forward link alphabet that has more symbols S_(F) than thereturn link alphabet S_(R).

[0028] Still referring to FIG. 1, the wireless communications aretransmitted from the at least two radioterminals 110 a and 110 b to atleast one antenna 122 at the base station 120 co-channel over the returnlink 130 using the return link alphabet. In some embodiments, the atleast one antenna 122 is at least one multiple-polarized antenna. Inother embodiments, the at least one antenna 122 is a plurality ofmultiple-polarized antennas.

[0029] In still other embodiments, the base station 120 includes aplurality of sectors using sectorization techniques that are well knownto those having skill in the art. In some embodiments, the at least oneantenna 122 comprises a plurality of multiple-polarized antennas in asingle sector of the base station, such that wireless communications aretransmitted from the at least two radioterminals 110 a and 110 b to theplurality of multiple-polarized antennas in the single sector of thebase station 120 co-channel over the return link 130 using the returnlink alphabet. In other embodiments, the wireless communications fromthe at least two radioterminals 110 a and 110 b are transmitted to aplurality of multiple-polarized antennas 122 in the sector of the basestation 120 co-channel over the return link 130 using the return linkalphabet if the at least two radioterminals are separated by more than apredetermined distance D. In still other embodiments, the wirelesscommunications are transmitted from the at least two radioterminals 110a and 110 b to at least one multiple-polarized antenna 122 in at leasttwo sectors of the base station 120 co-channel over a return link usingthe return link alphabet.

[0030]FIG. 2 is a diagram of co-channel wireless communications usingnonsymmetrical alphabets according to other embodiments of the presentinvention. As shown in FIG. 2, the base station 120 is a first basestation. Wireless communications are transmitted from at least tworadioterminals 110 a and 110 b to at least one multiple-polarizedantenna 122 at the first base station and at least onemultiple-polarized antenna 222 at a second base station 220 co-channelover a return link 130 using a return link alphabet. In any of theembodiments of FIGS. 1 and/or 2, wireless communications may betransmitted from a single linearly-polarized antenna 112 a, 112 b ateach of the at least two radioterminals 110 a, 110 b to the base station120, 220 co-channel over the return link 130 using the return linkalphabet.

[0031] Accordingly, some embodiments of FIGS. 1 and 2 allow co-channeltransmissions from radioterminals to a base station using a smallelement alphabet in conjunction with non-co-channel transmissions fromthe base station to the radioterminals using a larger element alphabet.The number of antenna elements at the base station may be operativewithin a given sector of a base station, distributed over more than onesector of a base station and/or distributed over a plurality of basestations. As such, intra-sector co-channel return link communicationsmay be provided, as well as inter-sector and inter-base station returnlink co-channel communications, to provide potentially improved capacitycharacteristics. Moreover, in some embodiments, intra-sector co-channelcommunications between two or more radioterminals and a base station mayonly be allowed in response to a distance D between the radioterminals.Since the system can know the position of the radioterminals, based on,for example, GPS or other techniques, radioterminals that are, forexample, D meters or more apart may be allocated co-channel resources.Otherwise, non-co-channel resources may be allocated. The distance D maybe selected so as to provide sufficient multipath differentiation fromthe signals that originate from the two radioterminals that aretransmitting co-channel.

[0032]FIG. 3 is a diagram of co-channel wireless communications usingnonsymmetrical alphabets according to still other embodiments of thepresent invention. As shown in FIG. 3, wireless communications aretransmitted from at least two radioterminals 310 a, 310 b to a basestation 320 over a return link 330 using a return link alphabet havingreturn link symbols S_(R). Wireless communications are also transmittedfrom the base station 320 to the at least two radioterminals 310 a, 310b co-channel over a forward link 340 using a forward link alphabethaving forward link symbols S_(F), wherein the forward link alphabet hasmore symbols than the return link alphabet. In other words, S_(F)>S_(R).

[0033] Embodiments of FIG. 3 may be employed where it is desirable torelay much more data to the radioterminals 310 a, 310 b from the basestation 320 than to the base station 320 from the radioterminals 310 a,310 b. This may be the case when the radioterminals may be receivinglarge files from the base station, whereas the radioterminals are onlysending back mouse clicks and/or other small amounts of data.Embodiments of FIG. 3 use a larger element alphabet in conjunction withco-channel communications to serve two or more terminals, while theradioterminals use a smaller element alphabet and may communicatenon-co-channel with the system. In other embodiments, wirelesscommunications are transmitted from the at least two radioterminals 310a, 310 b to the base station 320 co-channel over the return link 330using the return link alphabet.

[0034] Still referring to FIG. 3, in some embodiments, the wirelesscommunications are transmitted from the base station 320 to at least oneantenna 312 a, 312 b at each of the at least two radioterminalsco-channel over the forward link using the forward link alphabet thathas more symbols than the return link alphabet. In some embodiments, theat least one antenna 312 a, 312 b comprises at least onemultiple-polarized antenna. In other embodiments, the at least oneantenna 312 a, 312 b comprises a plurality of multiple-polarizedantennas. In other embodiments, the at least one antenna 322 at the basestation 320 comprises at least one linearly-polarized antenna, at leasttwo linearly-polarized antennas, at least two linearly-polarizedantennas in a single sector and/or a linearly-polarized antenna in atleast two sectors, as was described above in connection with theantennas 122 of FIG. 1. In still other embodiments, transmissions mayoccur to at least one linearly-polarized antenna at a first base stationand at a second base station, as was described above in connection withFIG. 2.

[0035]FIG. 4A is a diagram of co-channel wireless communicationsaccording to yet other embodiments of the present invention. As shown inFIG. 4A, wireless communications are received from a base station 420 ata first radioterminal 410 a and at at least one second radioterminal 410b that is proximate the first radioterminal 410 a, over a forward link440, co-channel. The wireless communications from the at least onesecond radioterminal 410 b are relayed to the first radioterminal 410 aover a short-range wireless link 450. The short-range wireless link maybe based on Bluetooth and/or other technologies such as 802.11, UWB,etc. The first radioterminal 410 a uses the wireless communications thatare relayed to the first radioterminal 410 a from the at least onesecond radioterminal 410 b over the short-range wireless link 450, toprocess the wireless communications that are received from a basestation 420 at the first radioterminal 410 a over the forward link 440.

[0036] Accordingly, in embodiments of FIG. 4A, the signals from one ormore proximate radioterminals may be used to improve a quality measuresuch as a bit error rate, of the information that is being received fromthe base station 420. It will also be understood by those having skillin the art that embodiments of FIG. 4 need not use a forward linkalphabet that has more symbols than a return link alphabet. However, inother embodiments of the invention, embodiments of FIG. 4 may be usedwith any of the embodiments of FIGS. 1-3, including the use of a forwardlink alphabet that has more symbols than a return link alphabet,co-channel communications from the radioterminals 410 a, 410 b to thebase station 420, and antenna configurations for the base station 422and for the radioterminal antennas 412 a, 412 b similar to thosedescribed in connection with FIGS. 1-3.

[0037]FIG. 4B is a diagram of co-channel wireless communications usingnonsymmetrical alphabets according to still other embodiments of thepresent invention. Referring to FIG. 4B, wireless communications arebi-directionally transmitted co-channel in Time Division Duplex (TDD)450. Time division duplex transmission is well known to those havingskill in the art, and need not be described further herein. As shown inFIG. 4B, bidirectional transmission co-channel in time division duplexproceeds from at least two radioterminals 460 a, 460 b to a base station470 over a return link using a return link alphabet, and from the basestation 470 to the at least two radioterminals 460 a, 460 b over aforward link using a forward link alphabet that has more symbols thanthe return link alphabet. The antennas 462 a, 462 b of the first andsecond radioterminals 460 a, 460 b may be configured as was described inFIGS. 1-4A above. Moreover, the antenna or antennas 472 of the basestation 470 may be embodied as was described above in any of FIGS. 1-4A.

[0038] Additional discussion of co-channel wireless communicationsaccording to various embodiments of the invention now will be provided.Specifically, in accordance with “non-Time Division Duplex” (non-TDD)embodiments, the receiver of a radioterminal and the receiver of a BTSmay be configured to operate on a plurality of signals that may beacquired via a plurality of spatially-separated and/or co-locatedantennas. The transmitter of a radioterminal may use a single antenna.The BTS may transmit the information that is intended for a firstradioterminal from a first antenna and the information that is intendedfor a second radioterminal from a second antenna that may bespatially-separated from the first. The two radioterminals may use thesame return-link channel resource(s) to transmit information to the BTS.The BTS may use the same forward-link channel resource(s) to transmitinformation to the two radioterminals. FIGS. 5A and 5B illustrateantenna configurations of non-TDD embodiments. It will also beunderstood that some embodiments of FIGS. 5A and 5B may be used in TDDmode as well.

[0039] Those skilled in the art will recognize that the M dual-polarized(or cross polarized) receiver antennas 512 of a radioterminal 510, asillustrated in FIG. 5B, may be replaced by M triple (x, y, z)-polarized,linearly-polarized, circularly-polarized and/or other type of receiverantennas. In some embodiments, only some of the M dual-polarizedreceiver antennas 512 of a radioterminal 510, as illustrated in FIG. 5B,may be replaced with triple-polarized, linearly-polarized,circularly-polarized, and/or other type of antennas, and that the valueof M may be different for different radioterminals. In still otherembodiments, only one receiver antenna that has been tapped at differentpoints may be used on a radioterminal to provide a plurality of signalinputs to the radioterminal's receiver. It will also be understood bythose of skill in the art that the N dual-polarized receiver antennas540 of a BTS, as illustrated in FIG. 5A, may be replaced in part or inentirety by triple (x, y, z)-polarized, linearly-polarized,circularly-polarized, and/or other type of receiver antennas. Finally,those having skill in the art will also recognize that one or both ofthe linearly-polarized transmitter antennas 520 of a BTS, as illustratedin FIG. 5B, may be replaced by a dual- or multi-dimensionally-polarized,circularly-polarized and/or other type of transmitter antenna(s) andthat the linearly-polarized transmitter antenna 532 of a radioterminal530 may be replaced by a dual-polarized, multi-dimensionally-polarized,circularly-polarized and/or other type of transmitter antenna.

[0040] Those having skill in the art will also recognize thatembodiments of FIGS. 5A and 5B may be extended to accommodate Lco-channel radioterminals (L>2) by having L transmitter antennas 520 onthe BTS with the λ^(th) such antenna (λ=1, 2, . . . , L) transmittinginformation intended for a corresponding λ^(th) radioterminal.

[0041] Referring now to FIG. 5C, in environments of dense radioterminalcommunications, such as in airports, convention centers, shopping malls,etc., one or more radioterminals 550 b-550 n that is/are proximate to afirst co-channel radioterminal 550 a may be configured to providesignals to the first receiving co-channel radiotenrinal 550 a. Thesesignals may be relayed from the one or more proximate radioterminals 550b-550 n to the first receiving co-channel radioterminal 550 a viashort-range wireless links 552. The first receiving co-channelradioterminal 550 a may be configured to process the signals receivedfrom the one or more proximate radioterminals so as to improve a qualitymeasure, such as the Bit Error Rate (BER), of the information that isbeing received from the BTS. Still referring to FIG. 5C, one or moreradioterminals 550 b′-550 n′ that is/are proximate to a secondco-channel radioterminal 550 a′, may be configured to provide signals tothe second receiving co-channel radioterminal 550 a′. These signals maybe relayed from the one or more proximate radioterminals 550 b′-550 n′to the second receiving co-channel radioterminal 550 a′ via short rangewireless links 552. The second receiving co-channel radioterminal 550 a′may be configured to process the signals received from the one or moreproximate radioterminals, so as to improve a quality measure such as theBER of the information that is being received from the BTS. Accordingly,two or more radioterminals such as radioterminals 550 a and 550 a′ mayoperate co-channel. It also will be understood that some embodiments ofFIGS. 5C may be used in TDD mode as well.

[0042] A linear receiver processor, in accordance with the well-knownLeast Mean Squared Error (LMSE) criterion, is illustrated in FIG. 6A fornon-TDD embodiments. Those skilled in the art will recognize that otherlinear and/or non-linear receiver processors such as, for example,Kalman-based, least squares, recursive least squares, Zero Forcing (ZF)and/or Maximum Likelihood Sequence Estimation (MLSE) etc, may be used inlieu of and/or in combination with the receiver processor of FIG. 6A. Italso will be understood that FIG. 6A illustrates a receiver for a BTS,but the principles and architecture may also be applied to aradioterminal.

[0043] In accordance with the illustrative BTS receiver antenna array540 of FIG. 5A, each antenna of the array 540 operates in two spatialdimensions and provides two signals to the receiver: one correspondingto the first spatial dimension “vertically-polarized” and the othercorresponding to the second spatial dimension “horizontally-polarized.”Thus, in accordance with the receiver antenna array that is illustratedin FIG. 5A, the i^(th) antenna (i=1, 2, . . . , N) provides the receiverwith the signal inputs V_(i) and H_(i). As is illustrated in FIG. 6A,each signal of the set {V₁, H₁, V₂, H₂, . . . , V_(N), H_(N)} isoperated on by two transversal filters 610 a, 610 b; one for eachco-channel source (radioterminal). The transversal filter outputs aresummed at 620 a, 620 b, to produce an output signal S′j (j=1, 2) basedon which a decision is made at Blocks 630 a, 630 b regarding theinformation symbol that has been transmitted by the j^(th) co-channelsource. The transversal filters may be fractionally spaced,synchronously spaced, or single tap filters.

[0044] A computer simulation has been developed to assess the potentialefficacy of the receiver of FIG. 6A. FIG. 7 graphically illustratesresults of the computer simulation. The simulation modeled twoco-channel radioterminals each transmitting independent data usingBinary Phase Shift Keyed (BPSK) modulation with no Forward ErrorCorrection (FEC) coding. The computer simulation modeled burstytransmission to emulate GSM. Within each burst of data, the channel wasassumed static and an a priori known to the receiver training sequence(the burst mid-amble in GSM terminology) was used to estimate thetransversal filter coefficients of the receiver. For each burst of dataa new Rayleigh fading channel was picked pseudo-randomly. FlatRayleigh-fading channels were assumed. Consequently, there was noInter-Symbol Interference (ISI), only non-dispersive Co-channelInterference (CCI) due to the co-channel radioterminal. Thus, thereceiver transversal filters reduced to single coefficient devices. TheBit Error Rate (BER) was evaluated for several receiver antennaconfigurations as described below.

[0045] As shown in FIG. 7, for the case of four dual-polarized receiverantennas, the uncoded Rayleigh-faded channel BER for each co-channelradioterminal, at EbNo of 4 dB, is ˜10⁻³, whereas the BER of classicalBPSK in Additive White Gaussian Noise (AWGN) with no fading, at the sameEb/No of 4 dB is ˜10−2. Thus, the simulations appear to show that notonly has the receiver of FIG. 6A reduced the CCI, but significantdiversity gain has also been attained.

[0046] To potentially improve further on the receiver performance ofFIG. 6A, a receiver architecture of FIG. 6B may be used. The receiver ofFIG. 6B uses an estimate of the co-channel signal that has minimum noiseand/or interference variance to cancel the CCI in the other co-channelsignal, thus reducing or minimizing noise enhancement in the otherco-channel signal, since a regenerated noise-free estimate of the CCImay now be used in the cancellation. Referring again to FIG. 6A, thenoise and/or interference variance of the two co-channel decisionvariables S′₁ and S′₂ may be estimated once per “data burst.” Theduration of the data burst may be chosen small relative to therate-of-change of the channel state so as to validate a static (orquasi-static) channel assumption over a given data burst. The estimateof noise and/or interference variance of S′_(j) (j=1, 2) may, forexample, be based on the magnitude of a linear superposition of squaredtransversal filter weights, that may be involved in forming S′_(j) ormay be based on processing of an a priori known to the receiver,training sequence. In the illustrative example of FIG. 6B, the noiseand/or interference variance of S′₁ has been found to be smaller thanthe noise and/or interference variance of the second decision variable,S′₂. Thus, the decision that is made on S′₁, assumed correct, may beused to form an improved decision variable S″₂, based on which adecision or a series of decisions may be made regarding the dataelements transmitted by the second co-channel radioterminal.

[0047] It will be understood by those of skill in the art that, in theillustrative receiver processing of FIG. 6B, if the second decisionvariable was found to have lower noise and/or interference variance, adecision on that variable may have been made and that decision may havebeen used to form an improved first decision variable. It will also beunderstood by those skilled in the art that the principle and receiverarchitecture that is illustrated on FIG. 6B, of first deciding on theleast noise and/or interference variance variable and then using thatdecision to improve the noise and/or interference variance of the seconddecision variable, may be extended similarly to the general case wherethere are L co-channel radioterminals and, therefore, L decisionvariables at the receiver. In that case, the one (out of the L) decisionvariable with minimum noise and/or interference variance will beidentified, a decision on it will be made, and that decision will beused to improve the noise and/or interference variance of the secondleast noise and/or interference variance variable. Then, a decision onthe improved second least noise and/or interference variance variablewill be made and now both decisions that have been made thus far can beused to improve the decision variable of the third least noise and/orinterference variance variable, etc. Finally, it will be understood thateven though the receiver principles and architectures of FIGS. 6A and 6Bhave been described using nomenclature associated with a BTS, theprinciples and receiver architectures of FIGS. 6A and 6B, and variationsthereof, are also applicable to the radioterminal.

[0048]FIG. 8 illustrates two radioterminals communicating co-channelbidirectionally with a BTS in a TDD mode according to other embodimentsof the present invention. When the radioterminals 830 transmitinformation to the BTS antennas 840, a BTS receiver of FIG. 6A and/or 6Bmay be used to process the received waveforms, as was already described,and make decisions on the data that has been transmitted co-channel tothe BTS antennas 840 by the radioterminals 830. This function isillustrated by Block 910 of FIG. 9. The BTS receiver of FIG. 9 may alsobe configured to perform processing of the received waveforms inaccordance with the well-known zero-forcing criterion thereby “forcingto zero”, to the extent that digital quantization effects and/or otherimplementation constraints may allow, the ISI and the CCI, at least overthe span of the transversal filters used. This function is illustratedby Block 920 of FIG. 9 and is further illustrated in greater detail inFIG. 10.

[0049] Over the time interval of a TDD frame, the state of the channelmay be assumed static or quasi-static provided that the TDD frameinterval has been chosen sufficiently small. Thus, capitalizing on thereciprocity of the TDD channel over its static or quasi-static intervalthe transversal filter coefficients that have been derived by the BTSreceiver to yield “zero” ISI and CCI at the BTS, may be used to processor pre-distort a BTS data vector d prior to transmitting it to theco-channel radioterminals. In TDD, the same BTS antenna array may beperforming both receive and transmit functions. This function isillustrated by Block 930 of FIG. 9 and is further illustrated in greaterdetail in FIG. 11. It also will be understood that some embodiments ofFIG. 8 may be used in non-TDD mode, as well.

[0050] Given the above, the information that is transmitted by a BTS,co-channel, for a plurality of radioterminals, can arrive at theplurality of co-channel radioterminals free, or substantially free, ofISI and CCI. Thus, the receiver complexity of a radioterminal may bereduced and the radioterminal may only be equipped with a singlelinearly-polarized receiver antenna. Those skilled in the art willrecognize that even in TDD mode the principles and receiverarchitectures that were described earlier for the non-TDD case can applyfor both a BTS and a radioterminal. Also, those skilled in the art willrecognize that the zero-forcing processing at a BTS receiver asillustrated in FIGS. 9 and 10 may be omitted and instead, thetransversal filter coefficients derived from a LMSE processor (Block 910of FIG. 9) may be used for the transmitter processing (Block 930 of FIG.9) of a BTS. Accordingly, information that is received when wirelesslyreceiving at least two signals on the same carrier frequency, timeinterval, and/or code, from a corresponding at least two radioterminals,may be discriminated among the at least two signals.

[0051] Finally, it will be understood that, in all of the embodimentsthat have been described herein, a radioterminal may include atransceiver which itself includes a transmitter and a receiver, asillustrated in FIG. 12, which perform the transmitting and receivingoperations, respectively, that were described herein. The antenna of theradioterminal may be regarded as a component of the transceiver.Similarly, in all of the embodiments described herein, a base stationmay also include a transceiver which itself includes a transmitter and areceiver, as illustrated in FIG. 13, which perform the transmitting andreceiving operations, respectively, that were described herein. Theantenna of the base station may be regarded as a component of thetransceiver.

[0052] In the drawings and specification, there have been disclosedembodiments of the invention and, although specific terms are employed,they are used in a generic and descriptive sense only and not forpurposes of limitation, the scope of the invention being set forth inthe following claims.

What is claimed is:
 1. A wireless communication method comprising:transmitting wireless communications from at least two radioterminals toa base station co-channel over a return link using a return linkalphabet; and transmitting wireless communications from the base stationto the at least two radioterminals over a forward link using a forwardlink alphabet that has more symbols than the return link alphabet.
 2. Amethod according to claim 1 wherein transmitting wireless communicationsfrom the base station to the at least two radioterminals comprises:transmitting wireless communications from the base station to the atleast two radioterminals non-co-channel over a forward link using aforward link alphabet that has more symbols than the return linkalphabet.
 3. A method according to claim 1 wherein transmitting wirelesscommunications from at least two radioterminals to a base stationcomprises: transmitting wireless communications from at least tworadioterminals to at least one antenna at the base station co-channelover a return link using a return link alphabet.
 4. A method accordingto claim 1 wherein transmitting wireless communications from at leasttwo radioterminals to a base station comprises: transmitting wirelesscommunications from at least two radioterminals to at least onemultiple-polarized antenna at the base station co-channel over a returnlink using a return link alphabet.
 5. A method according to claim 1wherein transmitting wireless communications from at least tworadioterminals to a base station comprises: transmitting wirelesscommunications from at least two radioterminals to a plurality ofmultiple-polarized antennas at the base station co-channel over a returnlink using a return link alphabet.
 6. A method according to claim 1wherein the base station includes a plurality of sectors and whereintransmitting wireless communications from at least two radioterminals toa base station comprises: transmitting wireless communications from atleast two radioterminals to a plurality of multiple-polarized antennasin a sector of the base station co-channel over a return link using areturn link alphabet.
 7. A method according to claim 1 wherein the basestation includes a plurality of sectors and wherein transmittingwireless communications from at least two radioterminals to a basestation comprises: transmitting wireless communications from at leasttwo radioterminals to at least one multiple-polarized antenna in atleast two sectors of the base station co-channel over a return linkusing a return link alphabet.
 8. A method according to claim 1 whereinthe base station is a first base station and wherein transmittingwireless communications from at least two radioterminals to a basestation comprises: transmitting wireless communications from at leasttwo radioterminals to at least one multiple-polarized antenna at thefirst base station and at least one multiple-polarized antenna at asecond base station co-channel over a return link using a return linkalphabet.
 9. A method according to claim 6 wherein transmitting wirelesscommunications from at least two radioterminals to a plurality ofmultiple-polarized antennas in a sector of the base station co-channelover a return link using a return link alphabet comprises: selectivelytransmitting wireless communications from at least two radioterminals toa plurality of multiple-polarized antennas in a sector of the basestation co-channel over a return link using a return link alphabet ifthe at least two radioterminals are separated by more than apredetermined distance.
 10. A method according to claim 1 whereintransmitting wireless communications from at least two radioterminals toa base station comprises: transmitting wireless communications from asingle linearly-polarized antenna at each of the at least tworadioterminals to a base station co-channel over a return link using areturn link alphabet.
 11. A method according to claim 1 furthercomprising: decoding the wireless communications that are transmittedfrom the at least two radioterminals to the base station co-channel. 12.A wireless communication method comprising: transmitting wirelesscommunications from at least two radioterminals to a base station over areturn link using a return link alphabet; and transmitting wirelesscommunications from the base station to the at least two radioterminalsco-channel over a forward link using a forward link alphabet that hasmore symbols than the return link alphabet.
 13. A method according toclaim 12 wherein transmitting wireless communications from at least tworadioterminals to a base station comprises: transmitting wirelesscommunications from at least two radioterminals to a base stationco-channel over a return link using a return link alphabet.
 14. A methodaccording to claim 12 wherein transmitting wireless communications fromthe base station to the at least two radioterminals comprises:transmitting wireless communications from the base station to at leastone antenna at each of the at least two radioterminals co-channel over aforward link using a forward link alphabet that has more symbols thanthe return link alphabet.
 15. A method according to claim 12 whereintransmitting wireless communications from the base station to the atleast two radioterminals comprises: transmitting wireless communicationsfrom the base station to at least one multiple-polarized antenna at eachof the at least two radioterminals co-channel over a forward link usinga forward link alphabet that has more symbols than the return linkalphabet.
 16. A method according to claim 12 wherein transmittingwireless communications from the base station to the at least tworadioterminals comprises: transmitting wireless communications from thebase station to a plurality of multiple-polarized antennas at each ofthe at least two radioterminals co-channel over a forward link using aforward link alphabet that has more symbols than the return linkalphabet.
 17. A method according to claim 12 wherein transmittingwireless communications from the base station to the at least tworadioterminals comprises: transmitting wireless communications from atleast one antenna at the base station to the at least two radioterminalsco-channel over a forward link using a forward link alphabet that hasmore symbols than the return link alphabet.
 18. A method according toclaim 12 wherein transmitting wireless communications from the basestation to the at least two radioterminals comprises: transmittingwireless communications from at least one linearly-polarized antenna atthe base station to the at least two radioterminals co-channel over aforward link using a forward link alphabet that has more symbols thanthe return link alphabet.
 19. A method according to claim 12 whereintransmitting wireless communications from the base station to the atleast two radioterminals comprises: transmitting wireless communicationsfrom at least two linearly-polarized antennas at the base station to theat least two radioterminals co-channel over a forward link using aforward link alphabet that has more symbols than the return linkalphabet.
 20. A method according to claim 12 wherein the base stationincludes a plurality of sectors and wherein transmitting wirelesscommunications from at least two linearly-polarized antennas at the basestation to the at least two radioterminals comprises: transmittingwireless communications from at least two linearly-polarized antennas ina sector of the base station to the at least two radioterminalsco-channel over a forward link using a forward link alphabet that hasmore symbols than the return link alphabet.
 21. A method according toclaim 12 wherein the base station includes a plurality of sectors andwherein transmitting wireless communications from at least twolinearly-polarized antennas at the base station to the at least tworadioterminals comprises: transmitting wireless communications from atleast one linearly-polarized antenna in at least two sectors of the basestation to the at least two radioterminals co-channel over a forwardlink using a forward link alphabet that has more symbols than the returnlink alphabet.
 22. A method according to claim 12 wherein the basestation is a first base station and wherein transmitting wirelesscommunications from the base station to the at least two radioterminalscomprises: transmitting wireless communications from at least onelinearly-polarized antenna at the first base station and at least onelinearly-polarized antenna at a second base station to the at least tworadioterminals co-channel over a forward link using a forward linkalphabet that has more symbols than the return link alphabet.
 23. Amethod according to claim 12 further comprising: decoding the wirelesscommunications that are transmitted from the base station to the atleast two radioterminals co-channel.
 24. A wireless communication methodcomprising: receiving wireless communications from a base station at afirst radioterminal and at at least one second radioterminal that isproximate the first radioterminal, over a forward link, co-channel;relaying the wireless communications from the at least one secondradioterminal to the first radioterminal over a short-range wirelesslink; and using the wireless communications that are relayed to thefirst radioterminal from the at least one second terminal over theshort-range wireless link to process the wireless communications thatare received from the base station at the first radioterminal.
 25. Awireless communication method according to claim 24: wherein receivingwireless communications from a base station at a first radioterminal andat at least one second radioterminal that is proximate to the firstradioterminal, over a forward link, co-channel comprises receivingwireless communications from a base station at a first radioterminal andat at least one second radioterminal that is proximate to the firstradioterminal, over a forward link, co-channel using a forward linkalphabet; and wherein the method further comprises transmitting wirelesscommunications from the first radioterminal and at least one secondradioterminal to the base station co-channel using a return linkalphabet that has fewer symbols than the forward link alphabet.
 26. Amethod according to claim 25 wherein transmitting wirelesscommunications from the first radioterminal and at least one secondradioterminal to the base station co-channel using a return linkalphabet that has fewer symbols than the forward link alphabetcomprises: transmitting wireless communications from the firstradioterminal and at least one second radioterminal to at least oneantenna at the base station co-channel using a return link alphabet thathas fewer symbols than the forward link alphabet.
 27. A method accordingto claim 25 wherein transmitting wireless communications from the firstradioterminal and at least one second radioterminal to the base stationco-channel using a return link alphabet that has fewer symbols than theforward link alphabet comprises: transmitting wireless communicationsfrom the first radioterminal and at least one second radioterminal to aplurality of multiple-polarized antennas in a sector of the base stationco-channel using a return link alphabet that has fewer symbols than theforward link alphabet.
 28. A method according to claim 25 whereintransmitting wireless communications from the first radioterminal and atleast one second radioterminal to the base station co-channel using areturn link alphabet that has fewer symbols than the forward linkalphabet comprises: transmitting wireless communications from the firstradioterminal and at least one second radioterminal to at least onemultiple-polarized antenna in at least two sectors of the base stationco-channel using a return link alphabet that has fewer symbols than theforward link alphabet.
 29. A method according to claim 25 wherein thebase station is a first base station and wherein transmitting wirelesscommunications from the first radioterminal and at least one secondradioterminal to the base station co-channel using a return linkalphabet that has fewer symbols than the forward link alphabetcomprises: transmitting wireless communications from the firstradioterminal and at least one second radioterminal to at least onemultiple-polarized antenna at the first base station and at least onemultiple-polarized antenna at a second base station co-channel using areturn link alphabet that has fewer symbols than the forward linkalphabet.
 30. A method according to claim 27 wherein transmittingwireless communications from the first radioterminal and at least onesecond radioterminal to a plurality of multiple-polarized antennas in asector of the base station co-channel using a return link alphabet thathas fewer symbols than the forward link alphabet comprises: transmittingwireless communications from the first radioterminal and at least onesecond radioterminal to a plurality of multiple-polarized antennas in asector of the base station co-channel using a return link alphabet thathas fewer symbols than the forward link alphabet if the firstradioterminal and the at least one second radioterminal are separated bymore than a predetermined distance.
 31. A wireless communication methodcomprising: bidirectionally transmitting wireless communicationsco-channel in time division duplex from at least two radioterminals to abase station over a return link using a return link alphabet and fromthe base station to the at least two radioterminals over a forward linkusing a forward link alphabet that has more symbols than the return linkalphabet.
 32. A method according to claim 31 wherein bidirectionallytransmitting comprises: bidirectionally transmitting wirelesscommunications co-channel in time division duplex from at least tworadioterminals to at least one antenna at the base station over a returnlink using a return link alphabet and from the at least one antenna atthe base station to the at least two radioterminals over a forward linkusing a forward link alphabet that has more symbols than the return linkalphabet.
 33. A method according to claim 31 wherein bidirectionallytransmitting comprises: bidirectionally transmitting wirelesscommunications co-channel in time division duplex from at least tworadioterminals to at least one multiple-polarized antenna at the basestation over a return link using a return link alphabet and from the atleast one multiple-polarized antenna at the base station to the at leasttwo radioterminals over a forward link using a forward link alphabetthat has more symbols than the return link alphabet.
 34. A methodaccording to claim 31 wherein bidirectionally transmitting comprises:bidirectionally transmitting wireless communications co-channel in timedivision duplex from at least two radioterminals to a plurality ofmultiple-polarized antennas at the base station over a return link usinga return link alphabet and from the plurality of multiple-polarizedantennas at the base station to the at least two radioterminals over aforward link using a forward link alphabet that has more symbols thanthe return link alphabet.
 35. A method according to claim 31 wherein thebase station includes a plurality of sectors and wherein bidirectionallytransmitting comprises: bidirectionally transmitting wirelesscommunications co-channel in time division duplex from at least tworadioterminals to a plurality of multiple-polarized antennas in a sectorof the base station over a return link using a return link alphabet andfrom the plurality of multiple-polarized antennas in the sector of thebase station to the at least two radioterminals over a forward linkusing a forward link alphabet that has more symbols than the return linkalphabet.
 36. A method according to claim 31 wherein the base stationincludes a plurality of sectors and wherein bidirectionally transmittingcomprises: bidirectionally transmitting wireless communicationsco-channel in time division duplex from at least two radioterminals toat least one multiple-polarized antenna in at least two sectors of thebase station over a return link using a return link alphabet and fromthe at least one multiple-polarized antenna in the at least two sectorsof the base station to the at least two radioterminals over a forwardlink using a forward link alphabet that has more symbols than the returnlink alphabet.
 37. A method according to claim 31 wherein the basestation is a first base station and wherein bidirectionally transmittingcomprises: bidirectionally transmitting wireless communicationsco-channel in time division duplex from at least two radioterminals toat least one multiple-polarized antenna at the first base station and atleast one multiple-polarized antenna at a second base station over areturn link using a return link alphabet and from the at least onemultiple-polarized antenna at the first base station and the at leastone multiple-polarized antenna at the second base station to the atleast two radioterminals over a forward link using a forward linkalphabet that has more symbols than the return link alphabet.
 38. Amethod according to claim 35 wherein bidirectionally transmittingwireless communications co-channel in time division duplex from at leasttwo radioterminals to a plurality of multiple-polarized antennas in asector of the base station over a return link using a return linkalphabet and from the plurality of multiple-polarized antennas in thesector of the base station to the at least two radioterminals over aforward link using a forward link alphabet that has more symbols thanthe return link alphabet comprises: selectively bidirectionallytransmitting wireless communications co-channel in time division duplexfrom at least two radioterminals to a plurality of multiple-polarizedantennas in a sector of the base station over a return link using areturn link alphabet and from the plurality of multiple-polarizedantennas in the sector of the base station to the at least tworadioterminals over a forward link using a forward link alphabet thathas more symbols than the return link alphabet if the at least tworadioterminals are separated by more than a predetermined distance. 39.A method according to claim 31 wherein bidirectionally transmittingcomprises: bidirectionally transmitting wireless communicationsco-channel in time division duplex from a single linearly-polarizedantenna at each of the at least two radioterminals to at least oneantenna at the base station over a return link using a return linkalphabet and from the at least one antenna at the base station to thesingle linearly-polarized antenna at each of the at least tworadioterminals over a forward link using a forward link alphabet thathas more symbols than the return link alphabet.
 40. A method accordingto claim 31 further comprising: decoding the wireless communicationsthat are transmitted co-channel in time division duplex from the atleast two radioterminals to the base station and from the base stationto the at least two radioterminals.
 41. A base station comprising: areceiver that is configured to receive wireless communications from atleast two radioterminals co-channel over a return link using a returnlink alphabet; and a transmitter that is configured to transmit wirelesscommunications to the at least two radioterminals over a forward linkusing a forward link alphabet that has more symbols than the return linkalphabet.
 42. A base station according to claim 41 wherein thetransmitter is configured to transmit wireless communications to the atleast two radioterminals non-co-channel over the forward link using aforward link alphabet that has more symbols than the return linkalphabet.
 43. A base station according to claim 41 wherein the receiveris configured to receive wireless communications from at least tworadioterminals co-channel over a return link using a return linkalphabet at at least one antenna.
 44. A base station according to claim41 wherein the receiver is configured to receive wireless communicationsfrom at least two radioterminals co-channel over a return link using areturn link alphabet at at least one multiple-polarized antenna.
 45. Abase station according to claim 41 wherein the receiver is configured toreceive wireless communications from at least two radioterminalsco-channel over a return link using a return link alphabet at aplurality of multiple-polarized antennas.
 46. A base station accordingto claim 41 wherein the base station includes a plurality of sectors andwherein the receiver is configured to receive wireless communicationsfrom at least two radioterminals co-channel over a return link using areturn link alphabet at a plurality of multiple-polarized antennas in asector of the base station.
 47. A base station according to claim 41wherein the base station includes a plurality of sectors and wherein thereceiver is configured to receive wireless communications from at leasttwo radioterminals co-channel over a return link using a return linkalphabet at at least one multiple-polarized antenna in at least twosectors.
 48. A base station according to claim 41 wherein the receiveris further configured to decode the wireless communications that arereceived from the at least two radioterminals co-channel.
 49. A basestation comprising: a receiver that is configured to receive wirelesscommunications from at least two radioterminals over a return link usinga return link alphabet; and a transmitter that is configured to transmitwireless communications to the at least two radioterminals co-channelover a forward link using a forward link alphabet that has more symbolsthan the return link alphabet.
 50. A base station according to claim 49wherein the receiver is configured to receive wireless communicationsfrom at least two radioterminals co-channel over a return link using areturn link alphabet.
 51. A base station according to claim 49 whereinthe transmitter is configured to transmit wireless communications to theat least two radioterminals co-channel over a forward link using aforward link alphabet that has more symbols than the return linkalphabet at at least one antenna.
 52. A base station according to claim49 wherein the transmitter is configured to transmit wirelesscommunications to the at least two radioterminals co-channel over aforward link using a forward link alphabet that has more symbols thanthe return link alphabet at at least one linearly-polarized antenna. 53.A base station according to claim 49 wherein the transmitter isconfigured to transmit wireless communications to the at least tworadioterminals co-channel over a forward link using a forward linkalphabet that has more symbols than the return link alphabet at at leasttwo linearly-polarized antennas.
 54. A base station according to claim49 wherein the base station includes a plurality of sectors and whereinthe transmitter is configured to transmit wireless communications to theat least two radioterminals co-channel over a forward link using aforward link alphabet that has more symbols than the return linkalphabet at at least two linearly-polarized antennas in a sector.
 55. Abase station according to claim 49 wherein the base station includes aplurality of sectors and wherein the transmitter is configured totransmit wireless communications to the at least two radioterminalsco-channel over a forward link using a forward link alphabet that hasmore symbols than the return link alphabet at at least onelinearly-polarized antenna in at least two sectors.
 56. A base stationcomprising: a time division duplex transceiver that is configured toreceive wireless communications co-channel from at least tworadioterminals over a return link using a return link alphabet and totransmit wireless communications to the at least two radioterminals overa forward link using a forward link alphabet that has more symbols thanthe return link alphabet.
 57. A base station according to claim 56wherein the transceiver is configured to receive wireless communicationsco-channel from at least two radioterminals over a return link using areturn link alphabet and to transmit wireless communications to the atleast two radioterminals over a forward link using a forward linkalphabet that has more symbols than the return link alphabet at at leastone antenna.
 58. A base station according to claim 56 wherein thetransceiver is configured to receive wireless communications co-channelfrom at least two radioterminals over a return link using a return linkalphabet and to transmit wireless communications to the at least tworadioterminals over a forward link using a forward link alphabet thathas more symbols than the return link alphabet at at least onemultiple-polarized antenna.
 59. A base station according to claim 56wherein the transceiver is configured to receive wireless communicationsco-channel from at least two radioterminals over a return link using areturn link alphabet and to transmit wireless communications to the atleast two radioterminals over a forward link using a forward linkalphabet that has more symbols than the return link alphabet at aplurality of multiple-polarized antennas.
 60. A base station accordingto claim 56 wherein the base station includes a plurality of sectors andwherein the transceiver is configured to receive wireless communicationsco-channel from at least two radioterminals over a return link using areturn link alphabet and to transmit wireless communications to the atleast two radioterminals over a forward link using a forward linkalphabet that has more symbols than the return link alphabet at aplurality of multiple-polarized antennas in a sector.
 61. A base stationaccording to claim 56 wherein the base station includes a plurality ofsectors and wherein the transceiver is configured to receive wirelesscommunications co-channel from at least two radioterminals over a returnlink using a return link alphabet and to transmit wirelesscommunications to the at least two radioterminals over a forward linkusing a forward link alphabet that has more symbols than the return linkalphabet at at least one multiple-polarized antenna in at least twosectors.
 62. A base station according to claim 60 wherein thetransceiver is configured to selectively receive wireless communicationsco-channel from at least two radioterminals to the plurality ofmultiple-polarized antennas in the sector over a return link using areturn link alphabet if the at least two radioterminals are separated bymore than a predetermined distance.
 63. A base station according toclaim 56 wherein the time division duplex transceiver is furtherconfigured to decode the wireless communications that are receivedco-channel from the at least two radioterminals.
 64. A radioterminalcomprising: a transmitter that is configured to transmit wirelesscommunications to a base station over a return link using a return linkalphabet; and a receiver that is configured to receive at least twowireless communications from the base station co-channel over a forwardlink using a forward link alphabet that has more symbols than the returnlink alphabet.
 65. A radioterminal according to claim 64 wherein thereceiver is configured to receive at least two wireless communicationsfrom the base station co-channel over a forward link using a forwardlink alphabet that has more symbols than the return link alphabet at atleast one antenna.
 66. A radioterminal according to claim 64 wherein thereceiver is configured to receive at least two wireless communicationsfrom the base station co-channel over a forward link using a forwardlink alphabet that has more symbols than the return link alphabet at atleast one multiple-polarized antenna.
 67. A radioterminal according toclaim 64 wherein the receiver is configured to receive at least twowireless communications from the base station co-channel over a forwardlink using a forward link alphabet that has more symbols than the returnlink alphabet at a plurality of multiple-polarized antennas.
 68. Aradioterminal according to claim 64 wherein the receiver is furtherconfigured to decode at least one of the at least two wirelesscommunications that are received from the base station co-channel.
 69. Aradioterminal comprising: a receiver that is configured to receivewireless communications from a base station over a forward link, toreceive the wireless communications from at least one secondradioterminal over a short-range wireless link, and to use the wirelesscommunications that are received from the at least one second terminalover the short-range wireless link to process the wirelesscommunications that are received from the base station.
 70. Aradioterminal according to claim 69: wherein the receiver is configuredto receive wireless communications from the base station over a forwardlink using a forward link alphabet; and wherein the radioterminalfurther comprises a transmitter that is configured to transmit wirelesscommunications to the base station using a return link alphabet that hasfewer symbols than the forward link alphabet.
 71. A radioterminalcomprising: a time division duplex transceiver that is configured totransmit wireless communications to a base station over a return linkusing a return link alphabet and to receive wireless communications fromthe base station over a forward link using a forward link alphabet thathas more symbols than the return link alphabet.
 72. A radioterminalaccording to claim 71 wherein the time division duplex transceiver isconfigured to transmit wireless communications from a singlelinearly-polarized antenna to the base station over a return link usinga return link alphabet and to receive wireless communications from thebase station at the single linearly-polarized antenna over a forwardlink using a forward link alphabet that has more symbols than the returnlink alphabet.
 73. A radioterminal according to claim 71 wherein thetransceiver is further configured to decode the wireless communicationsthat are received from the base station over the forward link.